Heat oil in a large stock pot over medium-high heat. Add onion; sprinkle with 1 tsp salt and sauté until softened, about 5 to 10 minutes.
Remove casings from sausages; pull sausages apart into bite-sized pieces with your fingers. Add sausage to pot; cook, stirring often, until browned on all sides, about 10 minutes.
Add garlic; cook, stirring, 1 minute.
Add broth, squash, sage and nutmeg; increase heat to high and bring to a boil. Reduce heat to medium and simmer until squash is fork tender, about 10 minutes. Add beans; still and cook until heated through, about 10 minutes more.
Stir in lemon juice and remaining teaspoon salt. Serve garnished with cheese. Yields about 1 cup soup and 1/2 teaspoon cheese per serving.
Notes: Cut prep time by buying already cubed butternut squash. Freeze the sausage for an hour or two before use to make it easier to slice.